Screws known in the trade as "Tirefond or North American spike screws" are used principally to fasten a steel rail to a cross-tie made of either soft or hard wood. Such screws replace the common spike which has, for a long time, been used for fastening rails to their beds. One widely known method of making these screws is by a hot forging and hot rolling process. Such method is not only costly in terms of energy consumption and in space requirement but is not reliable in terms of accuracy and precision.
In forming screw threads by the thread milling process, there are two main methods which are both limited in their applicaton. One method consists in using a single cutter while the other involves the use of a multiple cutter. In each case, the cutter must revolve as fast as possible without, however, dulling the cutting edges excessively as the part on which the thread is milled is revolved at a very slow rate. In most cases, the cutter is set at the full depth of the thread groove and a single thread is accomplished in a single pass. In the case of a deep thread of coarse pitch, such as that of screws associated with the present invention, the use of several cuts is required, and it is practically impossible to maintain an identical thread crest width throughout the entire length of the screw forming operation, especially when a conical or taper threaded section on the screw is required.